Question

Which of the following does not happen in normal quiet exhalation?

• A. Contraction of internal intercostal muscles
• B. Relaxation of phrenic muscles
• C. Relaxation of external intercostal muscles
• D. Both $\left(2\right)$ & $\left(3\right)$

Answer 1

The correct option is D Both $\left(2\right)$ & $\left(3\right)$

Exhalation is a passive process because of the elastic properties of the lungs. During forced exhalation, internal intercostal muscles lower the rib cage and decrease thoracic volume while the abdominal muscles push up on the diaphragm which causes the thoracic cavity to contract.

So the correct answer is 'Relaxation of phrenic muscles and Relaxation of external intercostal muscles'.